In agreement with previous studies (11), mature monocytic AML cells of FAB-classes M4 and M5 co-expressed NOX2 and H2R, while leukemic cells recovered from patients with non-monocytic AML (FAB-M0, M1, and M2) cells did not (Figures 4A–D). The gene discussed is HRH2; the disease is acute myeloid leukemia.